1. Field of the Invention
The present invention relates generally to medical care and specifically to hemodialysis. More particularly, this invention concerns a device and method for feeding blood and dialytic liquid to a hemodialyzer.
2. Prior Art
For blood dialysis using a hollow fiber type of blood dialyzer, the flows of the blood and dialytic liquid passing through the dialyzer are fixed from the beginning to the end of dialysis. Usually, the dialyzer is provided with a red mark on the blood inlet port (the arterial header) and with a blue mark on the blood outlet port (the venous header). The inlet and outlet ports for dialytic liquid, on the other hand, are not particularly provided with any color mark but, in order to obtain sufficient dialytic efficiency, the dialytic liquid is generally passed countercurrently with respect to the blood.
In starting hemodialysis, the arterial and venous circuits of the blood circulation path are respectively connected to the arterial and venous blood ports of a dialyzer, and feed and discharge hoses for dialytic liquid are respectively coupled to the dialytic liquid inlet and outlet in the dialyzer. Thus, it is most unlikely that the blood circuits and dialytic liquid hoses, once connected to the associated ports, are removed from the dialyzer in the course of dialysis. In particular, it is impossible to attach and detach the blood circuits under dialysis to and from the dialyzer.
In the blood inlet and outlet ports or headers of a hollow fiber type of dialyzer, the blood is most likely to coagulate. This is because, where the blood is fed through a constricted inlet in a blood feeder to the inlet header having a large space, the blood is likely to stagnate due to the fact that the flow of the blood there suddenly becomes slow. This is also true of the outlet header.
So far, various approaches to preventing blood coagulation through the header portions have been proposed. For instance, some approaches have been set forth in Japanese Patent No. 1267833, JP-B-62-54510, JP-U-63-100051, etc., that are directed to improving the configurations of the header portions. However, all these approaches intended for improving header configurations are found to fail to solve the problem of blood coagulation problem through the header portions for various reasons, for instance, due to the facts that the quantity of the blood treated by actual dialysis lies in a wide range of 100 to 300 ml per minute, there is a difference in blood viscosity from person to person, and the blood viscosity changes overtime during the course of dialysis.
In order to re-use this dialyzer, it must be removed from its circuit and then cleaned by washing with special equipment.
Blood is likely to coagulate upon contact with foreign matter outside the body. Blood coagulation takes place outside the body, especially where the circulation flow of the blood becomes stagnant or slow. In the case of hemodialysis with a hollow fiber type of dialyzer, blood coagulation is likely to take place in a blood inlet header D-1 and a blood outlet header D-2 of a dialyzer 3 shown in FIG. 3. When the blood flows through the narrow inlet of 3 to 4 mm in inner diameter into the wide space of 20 to 60 mm in inner diameter, its flow suddenly becomes slow. In addition, the central blood stream flows linearly into fine, hollow fibers of about 200 .mu.m in inner diameter, but the blood flow is likely to stagnate on the periphery of the header, so that the blood can start to coagulate in a ring form from the periphery of the header. This blood coagulation then grows in the radially inward direction. In the hollow fibers that are clogged up by the coagulated blood layer, the inside blood will further tend to coagulate because the blood is not allowed to flow freely. Through the outlet header D-2, if not comparable to the inlet header, there is some blood coagulation on the periphery, again because there is a slow blood flow.
Blood, when there is less change in its flow pattern, is likely to coagulate early where its flow remains stagnant. The prevention of blood coagulation by varying the flow speed of blood and changing the flow pattern intermittently has already been proposed in JP-A-2-213702.
For recycling this dialyzer, it must be removed from its circuit. However, unless it is treated with the greatest care, it will be contaminated with various bacteria. In addition, this will possibly expose those who are engaged in medical care to a risk of bacterial infection.
A main object of the invention is to improve the approaches so far proposed by drastically changing a blood flow pattern to a dialyzer. According to the invention, this is achieved by intermittently changing the direction of blood flow to a dialyzer to the countercurrent direction, thereby preventing or inhibiting blood coagulation. In the process of blood coagulation, the blood's coagulating ingredients, fibrin and platelets, start to be deposited onto the periphery of the header and the surface of hollow fibers, and blood coagulation grows large around the deposits serving as nucleuses. According to the invention, the intermittent inversion of the blood flow direction enables such deposits to be peeled off, and this is much more effective for the prevention of blood coagulation than would be possible with a change in the blood flow pattern achieved merely by changing the speed of blood.